The present invention relates to an abrasion detector for a rapier band on a rapier loom, and more particularly relates to an improvement in detection of abrasion of a rapier band used for reciprocation of a rapier head on a rapier loom.
In general on a rapier loom, each weft is inserted into an open shed by means of a rapier head, i.e. an weft gripper, reciprocating in the weft direction. The rapier head is driven for reciprocation by a rapier band, i.e. a tape, which cooperates with an oscillating band wheel, i.e. a driving wheel.
In the following description, the term "critical abrasion" refers to a limit of abrasion of a rapier band beyond which the rapier band cannot exhibit its expected function. Generally, the critical abrasion of a rapier band is 1 mm or smaller. In practice, however, the critical abrasion of a rapier band is not fixed but more or less varies depending upon process conditions and/or user's requirements. The term "guide face" refers to the face of a rapier guide which causes abrasion of a rapier band through its direct surface contact.
A wide variety of systems have been developed for detection of abrasion of rapier bands. In most cases, some modifications are applied to rapier bands. One typical example disclosed in Japanese Patent Laid-open Hei. 2-14045 on "A strap for controlling movement of an weft gripper on a shuttleless loom. In the case of this prior art system, a strap is embedded in a rapier band while extending in the longitudinal direction of the latter. The strap is made of a material which allows transmission of optical, electric or magnetic signals. The system further includes a detection head which is arranged in a face to face relationship to the rapier band incorporating the above-described strap. The depth of the strap embedded in the rapier band is chosen so that the strap is exposed on the surface of the rapier band when abrasion of the latter exceeds the prescribed critical abrasion. Surface exposure of the strap is sensed by the detection head and translated into accurance of excessive abrasion.
In the case of this prior art system, incorporation of the separate strap into the rapier band causes significant rise in cost due to its complicated construction. Since a rapier band is a sort of consumative product, its high production cost is a serious disadvantage in marketing. Further, since the critical abrasion is in general very small in dimension, accuracy in detection is greatly swayed by accuracy in production of the strap and/or accuracy in incorporation of the strap in the rapier band. As a result, no high degree of reliability in detection is in general expected. The strap is embedded into the rapier band during production of the latter. Stated otherwise, the critical abrasion of the rapier band is fixed at the stage of production and no free adjustment by users is accepted.